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Biology is the study, or science, of life. It is concerned with the characteristics and behaviors of organisms, how species and individuals come into existence, and the interactions they have with each other and with the natural environment environment. Biology encompasses a broad spectrum of academic fields that are often viewed as independent disciplines. However, together they address the phenomenon of life over a wide range of scales.At the atomic and moleculemolecular scale, life is studied in the disciplines of molecular biology, biochemistry, and molecular genetics. At the level of the cell (biology)cell, it is studied in cell biology, and at multicellular scales, it is examined in physiology, anatomy, and histology. Developmental biology studies life at the level of an individual organism's development or ontogeny.Moving up the scale towards more than one organism, genetics considers how heredity works between parent and offspring. Ethology considers group behavior of more than one individual. Population genetics looks at the level of an entire population, and systematics considers the multi-species scale of lineages. Interdependent populations and their Habitat (ecology)habitats are examined in ecology and evolutionary biology. A speculative new field is astrobiology (or xenobiology), which examines the possibility of life beyond the Earth. ? Biology? studies the variety of life ''(clockwise from top-left)'' ''E. coli'', tree fern, gazelle, Goliath !beetle
Principles of biology - Unlike physics, biology does not usually describe systems in terms of objects which obey immutable physical laws described by mathematics. Nevertheless, the biological sciences are characterized and unified by several major underlying principles and concepts: universality, evolution, diversity, continuity, homeostasis, and interactions.
Universality: Biochemistry, cells, and the genetic code - the primary genetic material]]''Main articles LifeThe most salient example of biological universality is that allliving things share a common carbon-based biochemistry and in particular pass on their hereditycharacteristics via genetic material, which is based on nucleic acids such as DNA and which uses a common genetic code with only minor variations. Another universal principle is that all organisms (that is, all forms of life on Earth except for viruses) are made of cell (biology)cells. Similarly, all organisms share common developmental processes. For example, in most metazoan organisms, the basic stages of early embryoembryonic development share similar morphological characteristics and include similar genes.
Evolution: The central principle of biology - ''Main article EvolutionThe central organizing concept in biology is that all life has a common origin and has changed and developed through the process of evolution (see Common descent). This has led to the striking similarity of units and processes discussed in the previous section. Charles Darwin established evolution as a viable theory by articulating its driving force, natural selection (Alfred Russell Wallace is recognized as the co-discoverer of this concept). Genetic drift was embraced as an additional mechanism of evolutionary development in the modern synthesis of the theory. The evolutionary history of a species— which describes the characteristics of the various species from which it descended— together with its genealogical relationship to every other species is called its phylogeny. Widely varied approaches to biology generate information about phylogeny. These include the comparisons of DNA sequences conducted within molecular biology or genomics, and comparisons of fossils or other records of ancient organisms in paleontology. Biologists organize and analyze evolutionary relationships through various methods, including phylogenetics, phenetics, and cladistics (The major events in the evolution of life, as biologists currently understand them, are summarized on this evolutionary timeline).
Diversity: The variety of living organisms - of evolutionary treeall living things, based on rRNA gene data, showing the separation of the three domains bacteriumbacteria, archaea, and eukaryotes as described initially by Carl Woese. Trees constructed with other genes are generally similar, although they may place some early-branching groups very differently, presumably owing to rapid rRNA evolution. The exact relationships of the three domains are still being debated.]]Despite its underlying unity, life exhibits an astonishingly wide diversity in morphology, behavior, and life historylife histories. In order to grapple with this diversity, biologists attempt to classify all living things. Scientific classification seeks to reflect the evolutionary trees (phylogenetic trees) of the organism being classified. Classification is the province of the disciplines of systematics and taxonomy. Taxonomy places organisms in groups called taxa, while systematics seeks to define their relationships with each other. This clasification technique has evolved to reflect advances in cladistics and genetics, shifting the focus from physical similarities and shared characteristics to phylogenetics.Traditionally, living things have been divided into five kingdoms::Monera -- Protista -- Fungi -- PlantPlantae -- AnimalAnimalia However, many scientists now consider this five-kingdom system to be outdated. Modern alternative classification systems generally begin with the three-domain system::Archaea (originally Archaebacteria) -- BacteriumBacteria (originally Eubacteria) -- EukaryoteEukaryotaThese domains reflect whether the cells have nuclei or not, as well as differences in the cell exteriors. There is also a series of intracellular parasites that are progressively "less alive" in terms of metabolismmetabolic activity::virus (biology)Viruses -- Viroids -- Prions
Continuity: The common descent of life - ''Main article Common descentUp into the 19th century, it was commonly believed that life forms could appear spontaneously under certain conditions (see abiogenesis). This misconception was challenged by William Harvey's diction that "all life is from an egg" (from the Latin "Omne vivum ex ovo"), a foundational concept of modern biology. It simply means that there is an unbroken continuity of life from its initial origin to the present time.A group of organisms is said to share a common descent if they share a common ancestor. All organisms on the Earth have been and are descended from a common ancestor or an ancestral gene pool. This last universal common ancestor of all organisms is believed to have appeared about Timeline_of_evolution3.5 billion years ago. Biologists generally regard the universality of the genetic code as definitive evidence in favor of the theory of universal common descent (UCD) for all bacteriumbacteria, archaea, and eukaryotes (see: origin of life).
Homeostasis: Adapting to change - ''Main article HomeostasisHomeostasis is the ability of an open system to regulate its internal environment to maintain a stable condition by means of multiple dynamic equilibrium adjustments controlled by interrelated regulation mechanisms. All living organisms, whether unicellular or multicellular, exhibit homeostasis. Homeostasis manifests itself at the cellular level through the maintenance of a stable internal acidity (pH); at the organismic level, warm-blooded animals maintain a constant internal body temperature; and at the level of the ecosystem, as when atmospheric carbon dioxide levels rise and plants are theoretically able to grow healthier and remove more of the gas from the atmosphere. Biological tissueTissues and organ (biology)organs can also maintain homeostasis.
Interactions: Groups and environments - between clownfish of the genus Amphiprion that dwell among the tentacles of tropical sea anemones. The territorial fish protects the anemone from anemone-eating fish, and in turn the stinging tentacles of the anemone protects the anemone fish from its predators]]Every living thing interacts with other organisms and its natural environmentenvironment. One reason that biological systems can be difficult to study is that so many different interactions with other organisms and the environment are possible, even on the smallest of scales. A microscopic bacterium responding to a local sugar gradient is responding to its environment as much as a lion is responding to its environment when it searches for food in the African Savannasavannah. For any given species, behaviors can be co-operationco-operative, aggressionaggressive, parasiteparasitic or symbiosissymbiotic. Matters become more complex when two or more different species interact in an ecosystem. Studies of this type are the province of ecology.
Scope of biology - ''Main article List of biology disciplinesBiology has become such a vast research enterprise that it is not generally regarded as a single discipline, but as a number of clustered sub-disciplines. This article considers four broad groupings. The first group consists of those disciplines that study the basic structures of living systems: cell (biology)cells, genes etc.; the second group considers the operation of these structures at the level of tissues, organs, and bodies; the third group considers organisms and their histories; the final constellation of disciplines focuses on their interactions. It is important to note, however, that these boundaries, groupings, and descriptions are a simplified characterization of biological research. In reality, the boundaries between disciplines are fluid, and most disciplines frequently borrow techniques from each other. For example, evolutionary biology leans heavily on techniques from molecular biology to determine DNA sequences, which assist in understanding the genetic variation of a population; and physiology borrows extensively from cell biology in describing the function of organ systems.
Structure of life - depicting the various organelles and structures]]''Main articles Molecular biology, Cell biology, Genetics, Developmental biologyMolecular biology is the study of biology at a molecular level. This field overlaps with other areas of biology, particularly with genetics and biochemistry. Molecular biology chiefly concerns itself with understanding the interactions between the various systems of a cell, including the interrelationship of DNA, RNA, and protein synthesis and learning how these interactions are regulated. Cell biology studies the physiologyphysiological properties of cell (biology)cells, as well as their behaviors, interactions, and natural environmentenvironment. This is done both on a microscopemicroscopic and moleculemolecular level. Cell biology researches both single-celled organisms like bacteriumbacteria and specialized cells in multicellular organisms like humans.Understanding cell composition and how they function is fundamental to all of the biological sciences. Appreciating the similarities and differences between cell types is particularly important in the fields of cell and molecular biology. These fundamental similarities and differences provide a unifying theme, allowing the principles learned from studying one cell type to be extrapolated and generalized to other cell types.Genetics is the science of genes, heredity, and the variation of organisms. In modern research, genetics provides important tools in the investigation of the function of a particular gene, or the analysis of genetic interactions. Within organisms, genetic information generally is carried in chromosomes, where it is represented in the DNA sequencechemical structure of particular DNA molecules.Genes encode the information necessary for synthesizing proteins, which in turn play a large role in influencing (though, in many instances, not completely determining) the final phenotype of the organism.Developmental biology studies the process by which organisms grow and develop. Originating in embryology, modern developmental biology studies the genetic control of cell growth, cellular differentiationdifferentiation, and "morphogenesis," which is the process that gives rise to biological tissuetissues, organ (anatomy)organs, and anatomy. Model organisms for developmental biology include the round worm ''Caenorhabditis elegans'', the fruit fly ''Drosophila melanogaster'', the zebrafish ''Brachydanio rerio'', the mouse ''Mus musculus'', and the weed ''Arabidopsis thaliana''.
Physiology of organisms - ''Main articles Physiology, AnatomyPhysiology studies the mechanical, physical, and biochemical processes of living organisms by attempting to understand how all of the structures function as a whole. The theme of "structure to function" is central to biology. Physiological studies have traditionally been divided into plant physiology and animal physiology, but the principles of physiology are universal, no matter what particular organism is being studied. For example, what is learned about the physiology of yeast cells can also apply to human cells. The field of animal physiology extends the tools and methods of human physiology to non-human species. Plant physiology also borrows techniques from both fields. Anatomy is an important branch of physiology and considers how organ (biology)organ systems in animals, such as the nervous systemnervous, immune systemimmune, endocrine systemendocrine, respiratory systemrespiratory, and circulatory systemcirculatory systems, function and interact. The study of these systems is shared with medicinemedically oriented disciplines such as neurology and immunology.
Diversity and evolution of organisms - the evolution of a population of organisms is sometimes depicted as if travelling on a fitness landscape. The arrows indicate the preferred flow of a population on the landscape, and the points A, B, and C are local optima. The red ball indicates a population that moves from a very low fitness value to the top of a peak]]''Main articles Evolutionary biology, Botany, ZoologyEvolutionary biology is concerned with the origin and descent of species, as well as their change over time, and includes scientists from many taxonomytaxonomically-oriented disciplines. For example, it generally involves scientists who have special training in particular organisms such as mammalogy, ornithology, or herpetology, but use those organisms as systems to answer general questions about evolution. Evolutionary biology also makes use of paleontologypaleontologists, who use the fossil record to answer questions about the mode and tempo of evolution, as well as theoreticians in areas such as population genetics and evolutionary theory. In the 1990s, developmental biology re-entered evolutionary biology from its initial exclusion from the modern synthesis through the study of evolutionary developmental biology. Related fields which are often considered part of evolutionary biology are phylogenetics, systematics, and taxonomy.The two major traditional taxonomically-oriented disciplines are botany and zoology.Botany is the scientific study of plantplants. Botany covers a wide range of scientific disciplines that study the growth, reproduction, metabolism, morphogenesisdevelopment, phytopathologydiseases, and evolution of plant life.Zoology involves the study of animals, including the study of their physiology within the fields of anatomy and embryology. The common geneticsgenetic and developmental mechanisms of animals and plants is studied in molecular biology, molecular genetics, and developmental biology. The ecology of animals is covered under behavioral ecology and other fields.
Classification of life - The dominant classification system is called Linnaean taxonomy, which includes ranks and binomial nomenclature. How organisms are named is governed by international agreements such as the International Code of Botanical Nomenclature (ICBN), the International Code of Zoological Nomenclature (ICZN), and the International Code of Nomenclature of Bacteria (ICNB). A fourth Draft BioCode was published in 1997 in an attempt to standardize naming in these three areas, but it has yet to be formally adopted. The International Code of Virus Classification and Nomenclature (ICVCN) remains outside the BioCode.
Interactions of organisms - , a generalization of the food chain, depicting the complex interrelationships among organisms in an ecosystem]]''Main articles Ecology, Ethology, Behavior, BiogeographyEcology studies the distribution and abundance of lifeliving organisms, and the interactions between organisms and their natural environmentenvironment. The environment of an organism includes both its habitat, which can be described as the sum of local abiotic factors such as climate and geology, as well as the other the organisms that share its habitat. Ecological systems are studied at several different levels, from individuals and populations to ecosystems and the biosphere. As can be surmised, ecology is a science that draws on several disciplines.Ethology studies animal behavior (particularly of social animals such as primates and canidaecanids), and is sometimes considered a branch of zoology. Ethologists have been particularly concerned with the evolution of behavior and the understanding of behavior in terms of the theory of natural selection. In one sense, the first modern ethologist was Charles Darwin, whose book ''The expression of the emotions in animals and men'' influenced many ethologists.Biogeography studies the spatial distribution of organisms on the Earth, focusing on topics like plate tectonics, climate change, dispersal and migration, and cladistics.
History of the word "biology" - Formed by combining the Greek βίος ''(bios)'', meaning 'life', and λόγος ''(logos)'', meaning 'study of', the word "biology" in its modern sense seems to have been introduced independently by Gottfried Reinhold Treviranus (''Biologie oder Philosophie der lebenden Natur'', 1802) and by Jean-Baptiste Lamarck (''Hydrogéologie'', 1802). The word itself is sometimes said to have been coined in 1800 by Karl Friedrich Burdach, but it appears in the title of Volume 3 of Michael Christoph Hanov's ''Philosophiae naturalis sive physicae dogmaticae'': ''Geologia, biologia, phytologia generalis et dendrologia'', published in 1766.
History - ''Main articles: History of biology, History of medicine, History of genetics''Major discoveries in biology include: Cell theory Germ theory of disease Genetics Evolution DNA
Related topics - ''Main articles List of biology topics
External links - wikibooks wikibooksparWikiversitySchool of Biology rom.on.ca - ''BioCode'': A proposal for organism naming. ncbi.nlm.nih.gov - NCBI Open-Access BooksPhyloCode, ohiou.edutolweb.org - ''The Tree of Life'': A multi-authored, distributed Internet project containing information about phylogeny and biodiversity.bioone.org - BioOne Bioscience research journals.
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